Automatic handling and aeration of a stack of paper sheets

ABSTRACT

A method and apparatus for automated aerating and handling a sub stack of a stack of rectangular paper sheets where the sub stack is gripped near or at opposed corners of a common edge of the sub stack by means of two robotic grippers (A, B) having two opposed gripping fingers (A 1,  A 2,  B 1,  B 2 ), lifting and rotating the corners in mutually opposite first directions such that the work stack achieves an upwards concave form, gripping the corners by the robotic grippers (A, B), and rotating the grippers in second directions opposite to the first directions such that the upper sheet of the sub stack has a curvature smaller than the bottom sheet of the sub stack, preferably a substantially plane form.

The present invention relates to a method of handling and aerating awork stack of rectangular paper sheets in connection with use of thepaper sheets in a printing facility.

In the printing industry small stacks or work stacks, of paper sheets(e.g. 2-15 cm high) are separated and removed from a large or basicstack (e.g. 100 cm high) for future processing, for instance aligning,cutting, folding or printing.

During these future processing steps it is important that each sheetshould be able to be separated from the rest of the sheets individually.To achieve this, introduction of air (airing) between the individualsheets is essential to avoid that neighbouring sheets “stick” together.

The basic airing process is to bend the small stack of paper sheets, thework stack, in such a way that the curvature of the stack is larger atthe bottom side than at the top side, and hence a space is formedbetween all neighbouring sheets into which air is sucked whereby thetendency of neighbouring sheets to stick together is eliminated.

Now the work stack can be carried over to an aligning device, typicallya shaking box or vibration table, where the sheet edges can be alignedbecause of the aeration of the work stack.

This is very labour intensive and potentially harmful to the personperforming the lifting and flexing actions manually. Attempts have beenmade to automate this aeration process with unsatisfactory results.

Therefore, a main object of the invention is to automate the process ina more satisfactory manner so that the manual labour can be replaced bymechanical means.

According to the invention, this object is achieved by:

providing an automated device comprising first and second grippingdevices each provided with first and second mutually opposed fingersadapted to move towards and away from one another so as to be able togrip and release said work stack between them, each gripping devicebeing adapted for having at least four degrees of freedom, preferablyfive degrees of freedom and most preferably six degrees of freedom,

inserting said first finger of said first gripping device below thebottom sheet of said work stack and placing it at or near a first cornerof said work stack and inserting said first finger of said secondgripping device below said bottom sheet and placing it at or near asecond corner of said work stack, said first and second corners beinglocated on the same edge of said work stack,

lifting and rotating said first and second corners of said work stack bylifting said first and second gripping devices and rotating said firstand second gripping devices in first, mutually generally opposeddirections such that the portion of said work stack located between thetwo gripping devices forms an upwards concave body,

gripping said work stack by moving said second fingers into contact withthe top sheet of said work stack, and

rotating said first and second gripping devices in second directionsgenerally opposed to said first directions such that said top sheet isstretched between said gripping devices to achieve a form that is lessupward concave than the form of said bottom sheet and preferably toachieve a generally plane form of said top sheet.

Hereby, the sheets of paper in the work stack are aerated effectivelywithout any manual labour being involved.

According to the invention, said first and second fingers, duringlifting and rotation, extend at angles between 0 and 90 degrees relativeto said edge of the work stack, preferably between 10 and 80 degrees,more preferably between 30 and 60 degree, even more preferably between40 and 50 degrees and most preferably between 44 and 46 degrees.

Hereby it is attained that neighbouring sheets are displacedhorizontally relative to one another both parallel and at right anglesto said edge which also is of importance in preventing sheets fromsticking to one another.

Advantageously, said gripping devices may grip said work stack at pointslocated between 0 and 50 cm from the respective said corner, preferablybetween 0 and 30 cm, more preferably between 0 and 10 cm and mostpreferably between 0 and 5 cm.

According to the invention, said work stack may comprise a top portionof paper sheets of a basic stack of paper sheets and said first fingerof said first gripping device has a sharp leading edge to allowinsertion thereof into said basic stack without damaging the edges ofthe paper sheets, the method comprising the steps of:

inserting said first finger of said first gripping device into saidbasic stack such that a gap is created between the bottom paper sheet ofthe thus defined work stack and the top sheet of the rest of the basicstack,

inserting said first finger of said second gripping device into saidgap, and

moving said first finger of said second gripping device away from saidfirst finger of said first gripping device towards said second cornersuch that both said first fingers abut said bottom sheet.

Hereby the separation of the work stack from the basic stack takes placewithout damaging the edge of the sheets and that both fingers abut thesame, bottom, sheet of the work stack.

In a second aspect, the invention relates to an automated device forcarrying out the method according to the invention.

According to the invention, each of said gripping devices is mounted ona manipulator arm having at least four degrees of freedom, preferablyfive degrees of freedom and most preferably six degrees of freedom.

Hereby, the necessary motions of the griping devices can be achieved forgood aeration of the paper sheets in the work stack.

In a currently preferred embodiment of the invention said automateddevice comprises control means for controlling said manipulator armsindependently of one another.

Such a two-armed robot is believed to be the most efficient means tocarry out the method according to the invention.

According to the invention, each of said manipulator arms has at leastone rotatable joint, preferably two rotatable joints, more preferablythree rotatable joints and most preferably four rotatable joints suchthat at least one of said degrees of freedom of said first and secondgripping devices are provided by said rotatable arm joints, and each ofsaid manipulator arms is provided with at least one rotation actuatorand optionally at least one linear actuator.

In a third aspect, the invention relates to a system for aligning andaerating a work stack of rectangular paper sheets comprising a stack ofpaper sheets, an automated device as specified above and an inclinedvibration table for receiving said work stack for alignment of saidpaper sheets after the method specified above has been carried out.

In a final aspect, the invention relates to the use of an automateddevice having two independently controlled manipulator arms for carryingout the method specified above.

In the following, the invention will be explained more in detail withreference to the accompanying drawings that illustrate, solely by way ofexample, embodiments of the invention.

FIG. 1 is a schematic perspective view of a basic or original stack ofsheets of paper,

FIG. 2 shows the initiation of the separation of a work stack from thetop of the basic stack,

FIGS. 2-5 show the method of inserting the two lower gripping devicefingers and placing them in their respective positions near the cornersof the work stack,

FIG. 6 shows the lifting of the corners of the work stack,

FIG. 7 shows the gripping of the corners of the work stack,

FIG. 8 shows the “outward” rotation of the gripping devices with theresulting separation and aeration of the sheets.

FIG. 9 is a schematic perspective view of a two-armed robot according tothe invention inserting the two gripping devices at the bottom of thework stack,

FIG. 10 is a view of the same situation as FIG. 8 seen in the oppositedirection and in enlarges scale, and

FIGS. 11-12 illustrate the definition of Degrees of Freedom of a rigidbody.

The invention will be described in the following with reference to FIGS.1-12.

The “left” gripping device or gripper has a lower finger with a sharpedge to allow insertion thereof between sheets of paper in the largestack (see FIG. 2) without damaging the sheets. The “right” gripper hasa lower finger with a cylindrically shaped projection to allow movementbetween the sheets without damaging the sheets as explained below.

To perform the separation of the work stack from the main stack and theaeration of the work stack as well as delivery of the work stack to thealigning device, a.k.a. as the shaker box or the vibration table, in asatisfactory manner, the grippers should have at least four degrees offreedom, preferably five degrees of freedom and most preferably sixdegrees of freedom. The degrees of freedom of each gripping deviceshould preferably be independent of the degrees of freedom of the othergripping device.

In the context of this patent application degrees of freedom are definedin relation to a three dimensional coordinate system with X, Y and Zaxes as indicated in FIGS. 11 and 12. The first three degrees of freedomare movements parallel to the three axes, and the other three degrees offreedom are rotation around each of the three axes.

Furthermore, in the context of this patent application, the term papersheet is to be understood to cover any sheet of printable material be itof paper, plastic, cardboard, laminated paper and so on.

The steps to be taken by the two-armed robot are described below withreference to FIGS. 2-8:

-   -   1) Move the lower finger A1 of the “left” gripper close to the        left front corner of the basic stack of sheets    -   2) Move this lower finger upwards and inwards into the basic        stack (FIG. 2) to separate the smaller work stack from the        larger stack of paper sheets to create a gap to separate the        work stack from the larger stack by inserting the sharp edge        between two neighbouring sheets of paper. This upper sheet        collection is the small work stack of sheets to be manipulated.    -   3) Place a rounded projection B3 (see FIG. 10) of the lower        finger B1 of the “right” gripper in the gap between the lifted        work stack and the remaining stack (FIG. 3). Move this finger        sideways in the gap (FIG. 4) until the right foremost corner is        reached (FIG. 5) with the rounded projection gliding along the        sheets forming the gap without damaging them. This ensures that        both grippers work on the same collection of sheets.    -   4) Leave the grippers at the two opposed corners of the work        stack in a position as described more in detail below.    -   5) Lift them both and rotate the left one clockwise and the        right one counter-clockwise (FIG. 6) so that the work stack is        forced into an upwardly concave shape.    -   6) Close the upper fingers A2 and B2, respectively, towards the        lower fingers A1 and B1, respectively, of the two grippers so        that the two grippers now hold the work stack in the upwardly        concave shape by applying pressure on the top and bottom sheets        of the work stack (FIG. 7).    -   7) The left and right grippers A and B are now rotated        counter-clockwise and clockwise, respectively, (FIG. 8), so that        the upper sheet of the work stack is stretched out to a        substantially plane form while the lower sheet still forms an        upwardly concave shape. This movement will force the separation        of the sheets of paper. Air will be sucked in between the sheets        to help with the separation. In addition air can be blown into        the gaps between the sheets.    -   8) The gripped work stack is now properly aired and is moved for        further processing to a not shown shaker box or vibration table        for alignment.

The grabbing and aerating of the paper sheets are illustratedgraphically in the FIGS. 1-10.

Referring now to FIG. 1:

The original stack of paper sheets illustrates a stack of papers fromwhich a smaller work stack which has to be moved is to be separated. Thecoordinate system to the right defines the orientation and position ofthe stack and is used to describe the movements of the tools, thegrippers of the robot.

Referring now to FIG. 2:

Step 1: Move the lower, sharp edged finger A1 of the left gripper intothe vicinity of the corner of the large stack of papers.

Step 2: Move the lower finger A1 in an upwards and inwards direction inthe direction of the arrow 1, (e.g. with a direction vector ((x, y, z)(1, 1, 4) in the coordinate system in FIG. 2, i.e. utilizing the threedegrees of freedom along the three axes) from the start position at theleft foremost corner achieved during step 1.

The upward and inward motion of the lower finger A1 enters the stackbetween two sheets of paper, and creates a gap to select the work stackof sheets. The finger used for this is shaped with a sharp edge at itsend, and has edges that are rounded (not shown) to protect the sheets.

It should be noted that although the lower finger A of the left gripperis shown as inserted at the front left corner of the stack, it couldalso be inserted perpendicularly to the front edge of the stack(parallel to the Y axis) or perpendicularly to the left edge of thestack (parallel to the X-axis) as long as the insertion point is nearthe corner for creating the gap for inserting the lower finger B1 of theright gripper as described below.

FIG. 1 Illustrates the insertion of the right gripper's lower finger B1.

The lower finger B1 of the right gripper is moved perpendicularly to theedge of the stack into the gap created by step 2. The lower finger B1having a cylindrical or rounded projection B3 (see FIG. 10) is insertednext to the lower finger A1. This movement is indicated by the arrow 3and is in the y direction.

Referring now to FIG. 4:

The lower finger B1 is moved along the edge in the gap to separate thebottom sheet of the work stack from the top sheet of the remainingstack. This movement stops before the right corner of the stack. Thismove is indicated with the arrow 5 and is in the X direction.

The finger A1 is shown moved in the direction of arrow 4 so that it isgenerally parallel to the x axis.

Referring now to FIG. 5:

The rotation of finger B1 is around the z axis, and is shown around 90degrees so that it also is substantially parallel with the x axis. Therotation is indicated by the arrow 6.

Referring now to FIG. 6:

The lifting and rotation of the fingers A1 and B1 is indicated by arrows7 and 8, respectively. The movement is continued until the paper ispositioned as illustrated in FIG. 7. Hereby a shifting of the relativepositions of the sheets of paper in the stack is achieved and allows thesheets to be able to suck air between them, before the grippers areclosed by moving the upper fingers of each gripper into contact with theuppermost sheet of the work stack.

Referring now to FIG. 7:

After the rotation and lifting of the lower fingers A1 and B1 of thegrippers, both grippers are closed by moving fingers A2 and B2 towardsfinger A1 and B1, respectively such that the work stack is firmlygrasped by both grippers.

It should be pointed out that although the position of the fingers A1and B1 is shown in FIGS. 5-7 as being parallel with the X-axis, it iscurrently considered best that fingers extend at an angle to the X-axis(preferably tending towards the direction (XYZ) (−2, 2, 0)) because thiswill entail relative displacement of neighbouring sheets in thedirection of both the X-axis and the Y-axis before the grippers areclosed to abut both the top and bottom sheet of the work sheet as shownin FIGS. 7 and 8.

Referring now to FIG. 8:

When the grippers A and B are rotated back “outwards” in the directionof the arrows 9 and 10, i.e. gripper A counter-clockwise and gripper Bclockwise, while holding the paper stack firmly, the stack is furtheraerated because when bending the work stack of paper sheets in such away that the curvature of each sheet is larger on the outside than theinside air is sucked in between all neighbouring sheets. The rotation ofthe grippers may be repeated one or more times.

Referring now to FIGS. 9 and 10:

The Figures show a two-armed robot installation for separating, handlingand aerating a work stack of paper sheets. Each arm has six rotaryjoints with corresponding rotary actuators, where five of these jointsindicated by the symbol (*) are joints having an axis of rotationperpendicular to the longitudinal extent of the adjacent arm elementwhile one of the joints indicated by the symbol (**) has an axis ofrotation parallel to said longitudinal extent.

Further rotary joints with rotary actuators as well as telescopicelements with linear actuators can be incorporated for allowing furtherflexibility in the aerating manipulation of the work stack.

Some of the desired effect can be achieved by the grippers A and Bgripping the work stack at different locations on the same edge of thework stack but by far the best results are obtained if the two grippersgrip the work stack near or at two corners of the stack located on thesame edge of the stack as illustrated in FIGS. 7 and 8 (the front edgeviewed from the robot).

1. A method of handling and aerating a work stack of rectangular papersheets in connection with use of the paper sheets in a printingfacility, the method comprising the steps of: providing an automateddevice comprising first and second gripping devices each provided withfirst and second mutually opposed fingers adapted to move towards andaway from one another so as to be able to grip and release said workstack between them, each gripping device being adapted for having atleast four degrees of freedom, preferably five degrees of freedom andmost preferably six degrees of freedom, inserting said first finger ofsaid first gripping device below the bottom sheet of said work stack andplacing it at or near a first corner of said work stack and insertingsaid first finger of said second gripping device below said bottom sheetand placing it at or near a second corner of said work stack, said firstand second corners being located on the same edge of said work stack,lifting and rotating said first and second corners of said work stack bylifting said first and second gripping devices and rotating said firstand second gripping devices in first, mutually generally opposeddirections such that the portion of said work stack located between thetwo gripping devices forms an upwards concave body, gripping said workstack by moving said second fingers into contact with the top sheet ofsaid work stack, and rotating said first and second gripping devices insecond directions generally opposed to said first directions such thatsaid top sheet is stretched between said gripping devices to achieve aform that is less upward concave than the form of said bottom sheet andpreferably to achieve a generally plane form.
 2. A method according toclaim 1, wherein said first and second fingers, during lifting androtation extend at angles between 0 and 90 degrees relative to said edgeof the work stack, preferably between 10 and 80 degrees, more preferablybetween 30 and 60 degree, even more preferably between 40 and 50 degreesand most preferably between 44 and 46 degrees.
 3. A method according toclaim 1, wherein said gripping devices grip said work stack at pointslocated between 0 and 50 cm from the respective said corner, preferablybetween 0 and 30 cm, more preferably between 0 and 10 cm and mostpreferably between 0 and 5 cm.
 4. A method according to claim 1, whereinsaid work stack comprises a top portion of paper sheets of a basic stackof paper sheets and said first finger of said first gripping device hasa sharp leading edge to allow insertion thereof into said basic stackwithout damaging the edges of the paper sheets, the method comprisingthe steps of: inserting said first finger of said first gripping deviceinto said basic stack such that a gap is created between the bottompaper sheet of the thus defined work stack and the top sheet of the restof the basic stack, inserting said first finger of said second grippingdevice into said gap, and moving said first finger of said secondgripping device away from said first finger of said first grippingdevice towards said second corner such that both said first fingers abutsaid bottom sheet.
 5. An automated device for carrying out the methodaccording to claim
 1. 6. An automated device according to claim 5,wherein each of said gripping devices is mounted on a manipulator armhaving at least four degrees of freedom, preferably five degrees offreedom and most preferably six degrees of freedom.
 7. An automateddevice according to claim 6 comprising control means for controllingsaid manipulator arms independently of one another.
 8. An automateddevice according to claim 6, wherein each of said manipulator arms hasat least one rotatable joint, preferably two rotatable joints, morepreferably three rotatable joints and most preferably four rotatablejoints such that at least one of said degrees of freedom of said firstand second gripping devices are provided by said rotatable arm joints.9. An automated device according to claim 6, wherein each of saidmanipulator arms is provided with at least one rotation actuator andoptionally at least one linear actuator.
 10. A system for aligning andaerating a work stack of rectangular paper sheets comprising a stack ofpaper sheets, an automated device according to claim 5 and an inclinedvibration table for receiving said work stack for alignment of saidpaper sheets.
 11. Use of an automated device having two independentlycontrolled manipulator arms for carrying out the method according toclaim 1.